The Bugs of Winter: Microbial Control of Soil Biogeochemistry During the Arctic Cold Season

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

The real Arctic year is dominated by the 9 month long "cold season", which includes the period when the active layer is at its maximum depth and an extended period while soils are freezing and held at 0 degrees C. Cold-season CO2 fluxes are a substantial component of the annual carbon budget and cold-season nitrogen mineralization appears to dominate annual nitrogen mineralization. There are major shifts in microbial processes that occur between the growing and cold seasons, and they appear to occur above 0 degrees C. Cold-season processes are different from growing season processes. However, we don't understand cold season soil processes sufficiently to incorporate them into models of Arctic ecosystem functioning. Funds have been provided to analyze changing substrate use patterns in soils under Arctic cold season conditions. Specifically, the PI proposes: 1. to evaluate the size of the "winter-labile" substrate pool in each major soil layer, 2. to evaluate specific substrates that are used under thawed and cold conditions, and 3. to evaluate the relative importance of the different processes regulating substrate use. These likely include physics (temperature profiles), physical chemistry (recalcitrance-temperature responsiveness relationships), biophysics (microbial interactions with unfrozen water films), biochemistry (shifts in extracellular enzyme activities with temperature), and biology (changing microbial communities and physiological capacities). This research will include field measurements of CO2 flux from different soil horizons (organic, mineral) coupled to laboratory analysis of pools and controlling factors. Long-term lab bioassays will be used to evaluate the size of the "winter-labile" pool, 13C tracer studies to evaluate the processing of specific substrates (monomers and polymers) and how they change with temperature, enzyme potential assays to evaluate changing enzyme kinetics with temperature, NMR to measure unfrozen water curves and electron microscopy to evaluate how microbes (bacteria and fungi) interact with water films, 13C phospholipid fatty acid analyses to evaluate carbon flow into different components of the microbial community, and DNA and RNA fingerprinting to evaluate whether and how microbial communities change between the growing and cold seasons.